Challenge: Direction of travel and overtaking bans: D-signs and F-signs

Students often treat F1 and F3 as the same 'overtaking ban', and assume with D4-D7 that every code has a fixed direction, as with A- and B-signs. Both assumptions are exactly what the CBR exam designer builds a trick question on: it's not about the code alone, but about WHO the sign addresses and WHAT is literally shown on it.